The present invention relates to a front-end module having an antenna switch as a key component available in mobile communications apparatus such as a mobile telephone set and an automobile telephone set.
An antenna switch is disclosed in the Japanese Patent Publication No. 9-261110/(1997) proposed by the applicant of this invention is an example of a conventional front-end module for mobile communications apparatus. Most of the mobile telephone systems are set to different frequency bands between transmissions and receptions. Thus the element constant of such mobile telephone systems tend to differ between the transmission/reception selector and the antenna selector, although these circuits are similar to each other. In order to avoid disadvantages in a quick design, the antenna switch described in the Japanese Patent Publication No. 9-261110/(1997) has a selector circuit where one selector of the transmission/reception selector and the antenna selector and the other are symmetrical with respect to a low-pass filter.
The aforementioned example of the related art is an antenna switch used for mobile telephone sets of TDMA system and cannot be applied to telephone sets that cover two transmission/reception systems, such as the GSM dual-band mobile telephone sets in Europe. Thus a front-end module comprising a circuit for splitting two bands and mainly an antenna switch is in need. The multilayer substrate for the front-end module must comprise a great number of circuit elements. This complicates the design of the multilayer substrate, and easily invites interference between circuits and deformation in the laminating and firing processes, thus worsening the yield.
The invention aims at providing a multilayer-substrate front-end module covering a plurality of transmission/reception systems, wherein materials for layers composing circuit elements are optimized and a scaled-down multilayer substrate causes a negligible interference between circuits.
A front end module according to the first aspect of the invention is a front end module used for a plurality of different communications systems, comprising at least a band splitter circuit connected to an antenna, an antenna switch connected to the antenna via the band splitter circuit to switch the antenna to transmitter circuits and receiver circuits of different communications systems, and a filter for removing high frequencies, characterized in that the front end circuit constitute an integrated module with components mounted on a multilayer substrate, that said multilayer substrate arranges a pattern for a band splitter circuit at the center in the place direction, and that a plurality of antenna switch conductor patterns using different communications systems are symmetrically arranged with respect to the pattern for the band splitter circuit.
According to the second aspect of the invention, in the front end module according to the first aspect of the invention, said multilayer substrate is composed of a plurality of laminated dielectric layers, that the dielectric layers constituting said multilayer substrate are split into a plurality of dielectric layers laminated adjacently where coil conductor patterns are mainly formed, and a plurality of dielectric layers laminated adjacently where capacitor electrode patterns are mainly formed, and that said dielectric layers where coil conductor patterns are mainly formed select a material that shows a dielectric constant lower than that of said dielectric layers where capacitor electrode patterns are mainly formed.
According to the third aspect of the invention, in the front-end module according to the second aspect of the invention, the dielectric layers laminated adjacently where capacitor electrode patterns are mainly formed are provided beneath the dielectric layers laminated adjacently where coil conductor patterns are mainly formed and, that layers comprising a similar material to that of the dielectric layers where capacitor electrode patterns are mainly formed are provided on top of said dielectric layers where coil conductor patterns are mainly formed, in order to prevent deformation caused by the difference in the reduction ratio that accompanies firing.
According to the fourth aspect of the invention, in the front end module according to any of the first through third aspects of the invention, the antenna switch is composed of at least a diode and at least an LC circuit, and said filter and said band splitter circuit are composed of LC circuits, that said LC circuits are formed in said multilayer substrate, and that part of said LC circuits is connected to a diode arranged on the upper face of said multilayer substrate through a via hole.